1. Field of the Invention
The present disclosure relates to a differential cascode voltage-controlled oscillator for generating a local signal at a transceiver in a wireless communication system, and more particularly, to a cascode amplifier with negative conductance and a differential cascode voltage-controlled oscillator using the cascode amplifier, which can reduce a phase noise by the use of a quality factor enhancement technique and can mitigate a ground-caused noise effect by the use of a cascode connection technique.
This work was supported by the IT R&D program of MIC/IITA. [2006-S-071-02, Development of UWB Solution for High Speed Multimedia Transmission]
2. Description of the Related Art
Wireless communication systems mean communication means that is capable of transmitting information to destinations rapidly and accurately by the use of electromagnetic waves, thereby maximizing the value of the transmitted information. Examples of the wireless communication systems enumerate Wireless Personal Area Networks (WPANs) with a purpose for providing wireless connectivity within a short distance of up to 10 meters, Wireless Local Area Networks (WLANs) with a purpose for providing a higher data transmission rate and a wider service coverage area, and mobile communication systems for providing broadband mobile communication services using communication schemes such as CDMA, GSM and WCDMA.
Such wireless communication systems basically include a transmitter for converting information into radio-frequency (RF) signals and transmitting the RF signals wirelessly, and a receiver for receiving RF signals wirelessly and converting the received RF signals into baseband signals.
The transmitter has a voltage-controlled oscillator for generating a local signal, an exemplary circuit diagram of which is illustrated in FIG. 1.
FIG. 1 is a circuit diagram of a related art voltage-controlled oscillator in a wireless communication system.
Referring to FIG. 1, a related art voltage-controlled oscillator 110 includes resistors R1 through R6, an inductor L1, capacitors C3, C4, C6, C20 and C21, varactors CV1, CV2, CV3 and CV4, PMOS transistors M6 and M7, NMOS transistors M4 and M5, and a current source I1.
The voltage-controlled oscillator 110 functions as an LC voltage-controlled oscillator as follows.
The NMOS transistors M4 and M5 are connected in a complementary cross-coupled configuration. The NMOS transistors M4 and M5 amplifies an alternating current (AC) signal generated according to a control voltage VCN, and outputs the resulting signal to output terminals VCOOP and VCOON. Herein, the frequency of the AC signal changes depending on the capacitance values of the varactors CV1, CV2, CV3 and CV4 that vary with the control voltage VCN.
However, the related art voltage-controlled oscillator has a disadvantage that the phase noise characteristics thereof degrade because a noise component generated in the current source I1 exerts influence on the entire circuit.